Synopsis

Input Parameters

pc

- the preconditioner

n

- block size (default 1)

Notes: A block
size of 1 treats A as a matrix of scalar elements. A
block size of s > 1 treats A as a matrix of sxs
blocks. A block size of 0 treats A as a matrix with
variable sized blocks, which are determined by
searching for dense square diagonal blocks in A.
This can be very effective for finite-element
matrices.

SPAI will convert A to block form, use a block
version of the preconditioner algorithm, and then
convert the result back to scalar form.

In many cases the a block-size parameter other than 1
can lead to very significant improvement in
performance.